passive architectural design strategies …...passive design strategies for energy reduction four...

Dutse Journal of Pure and Applied Sciences (DUJOPAS) Vol. 4 No. 1 June 2018

Akaainjo, N. E, Abdullahi, A., DUJOPAS 4(1):486-497, 2018 486

PASSIVE ARCHITECTURAL DESIGN STRATEGIES

FOR REDUCING COOLING LOAD WITHIN ICT

FACILITIES IN TROPICAL HOT AND DRY

CLIMATE

Ngutor Elijah, Akaainjo Department of Architecture,

Ahmadu Bello University, Zaria, Nigeria.

Abubakar, Abdullahi Department of Architecture,

Ahmadu Bello University, Zaria, Nigeria.

Abstract

esigning with climate has always been a necessity and must always be given a major

consideration. This study is aimed at exploring the potential of using passive architectural

design strategies to reduce the cooling load in ICT buildings within the tropical hot and dry

climate of Nigeria. The research adopted mixed method; case study and quasi-experimental research

design, through the use of dynamic simulation as the main investigatory tool. One case building was

selected for analysis and five passive design strategies were applied. The performance of the case

building was accessed using a scientifically validated energy simulation software Eco-tech for the

parametric analysis of simulated results. Results showed that a significant reduction of cooling load

was achieved due to the application of the following passive design strategies: Double skinned façade

(47.2%), shading devices (26.5%), light colour coating (11.5%) and double glazing (15%)

respectively. Findings from the study shows that reduction in cooling demand are achieved due to the

minimising of external heat gain because of the integration of the passive design strategies. Finally,

the study recommends that materials for wall and roofs within the tropical hot and dry should have

low solar absorption rate.

Keywords: Designing with climate, cooling load, external heat gain, ICT buildings, passive

architectural design strategies,

INTRODUCTION

Background

Designing with climate has always been a necessity and must always be given a major

consideration. According to Steven, Lowell, Steve and Tom (2012), Change in weather

D



pattern usually affect energy demand, especially with increased peak electricity use of air

conditioning and energy supply, with reduced reliability and efficiency. Energy

consumption in buildings has become a central issue in global dialog towards sustainable

development (Mu'azu, 2012). The quest for reduction in energy consumption actually began

after the oil crisis of 1973, after which countries aimed to reduce global energy consumption

by mainly reducing the energy use in buildings for heating, cooling and ventilation (Antony

& Ruba, 2013). Studies over the years have shown that the built environment consume more

energy than other sectors in many parts of the world. According to Levine et al.( 2014),

buildings consume about 40% of the world energy production and contribute as much as

one-third the total global greenhouse gas emission. Of the 40% energy consumed by

buildings as stated above, 2% of it is consumed by ICT related buildings as a result of IT

equipment, cooling, air movement and lighting and as such ICT requires process cooling

system to remove excess heat (Peter & Ross, 2017).

Most buildings in Nigeria ICT building inclusive, hardly consider energy efficiency due to

ignorance, lack of awareness and/or improper policy on building regulations by

Government (Nwofe, 2014). Thus attention of researchers and professionals is directed

towards designing buildings which are able to reduce the energy consumption of

mechanical air conditioning systems by sustaining free-running conditions for a long period

(Givoni, 1994).

Problem Statement

ICT buildings consume about 2% energy out of the 40% total energy consumed by buildings,

which is as a result of internally generated heat and heat gain by building(Peter & Ross,

2017).

In developing countries like Nigeria, with poor energy infrastructure leading to epileptic

power supply, high electricity tariff and harsh climatic condition (notably excessive heat

from solar radiation mostly in the tropical hot and dry region) designing a building to house

ICT facilities will require special design considerations, being that the building will be

generating heat internally as well as gaining heat externally too.

This research therefore seek to explore the possibilities of reducing energy consumption by

exploring passive architectural strategies to reduce the cooling load of building housing ICT

facilities within the tropical hot and dry climate of Nigeria.

Aim and objectives

The aim of this paper is to explore the potential of selected passive architectural design

strategies in reducing cooling demand energy consumption in ICT buildings.

The aim of this research therefore, will be achieved through the following objectives:



i. To evaluate selected passive design strategies in reducing cooling load.

ii. To evaluate the reduction in energy consumption by using the selected passive

design strategies

LITERATURE REVIEW

Passive Design strategies for Energy reduction

Four passive strategies were applied to the base line model to serve as the independent

variables as discussed below

Double Façade

Terri- Meyer (2003), described double skin façade as a pair of glass skin seperated by an air

corridor which also incoporate the passive design strategies of natural ventilation, day

lightening and solar heat gain. Double façade was designed and introduced on the east-west

orientation of the base line model as shown in the Figure 1, when simulated it was able to

reduce 53% in the first case and 48.9% in the second case.

Figure 1: Double skinned facade introduced on base line model (Source: Authors, 2017)

There are various classifications of double skinned façade. Terri- Meyer (2003),described

three basic system types: Buffer System, Extract Air System and Twin Face System. The twin

face system was adopted for this study due to its flexibility in allowing for natural

ventilation and its ability to moderate temperature dissipations within the façade.

Building Orientation

Orientation refers to the placing of a building relative to seasonal variations in the sun’s path

as well as predominant wind patterns. A good orientation can enhance energy efficiency of a

building, by making it comfortable for the occupants while running at a cheaper cost in term

of energy consumption. The orientation of the building for energy efficiency depend to a

large extent on predominant climatic condition of the location. For example in the tropics,

the weather condition is very hot with very high solar intensity, which makes the orientation

of buildings most suitable in directions where the larger part of the building faces the North-



south orientation. This is to prevent or reduce the rate of building absorbing sun rays, which

help reduce the cooling load of the building (Chris, Max&Dick, 2013). This study however

laid more emphasis on the east-west orientation as shown in the Figure 2. In order to reduce

the effect of solar radiation on this axis the use of horizontal and vertical shading with

double skinned façade were introduced on the base line model which yeilded effective

result, reducing 53.8% of cooling load.

Figure2: Base line model placed in the east-west orientation(Source: Authors, 2017)

Shading Strategies

Shading is an important strategy for reducing solar heat gain especially through external

openings on the building envelope. It is a known fact that most of the solar heat gain comes

from the radiation through external openings on the building envelope. Hence, shading of

the building envelope and the openings on it from solar radiation using well designed

shading strategies and devices be of paramount importance in the tropical climate.

According to Singhal et al.(2013), when designing shading devices for windows, the

required horizontal shadow angles (HSA) and vertical shadow angles (VSA) need to be

established. These angles are important to determine the depth of a shading device over a

window and are dependant on both the oreintation of the window plane and the sun path as

shown in Figure 3.

Figure 0: HSA and VSA in relation to window plane.

(Source: (Singhal, Mukund, Rajiv, Biswajit, & Ujjainia, 2013)



Horizontal and vertical shading devices were designed with depth of 0.9m and 1.2m

respectively, and introduced on the base case model; a significant reduction of energy about

26.5% was recorded.

Light colour coating

Studies have shown that excessive amount of heat can be transmitted from the exterior walls

to the interior due to the exposure of the exterior wall to excessive solar radiation (Hui,

Hongwei, & Athanasios, 2010). This however, leads to increase cooling load. This study

employed the use of cooler (light)colors with low Solar absorption rate on the external wall

of the base case model, the result show a reduction in energy.

Double glazing

Glass is known to transmit some amount of heat when exposed to solar radiation. When

solar radiation strikes the glass surface, some amount of heat is absorbed, some is reflected.

The portion absorbed by the glass is reliant on the depth and the absorption coefficient of

the glass. The radiation absorbed is converted to heat on the interior thereby increasing the

temperature of the glass. However, when glass panel is double it further reduces the

absorption of the solar radiation on the inside. The glass used to double glaze the windows

and double skinned façade has a solar heat transmission of 0.75% with a Solar Heat Gain

Coefficient of 0.75 (SHGC=0.75), which is interpreted as good and effective in reducing the

amounth of heat gain.

A review of similar study

Hanan (2013), conducted a study ‘Using Passive Strategies to Improve Thermal Performance

and Reduce Energy Consumption of Residential Buildings in U.A.E. buildings. The aim of

the study was to test the usefulness of applying selected passive cooling strategies to

improve thermal performance and reduce energy consumption of residential buildings in

hot arid climate. The study adopted simulation as the main investigatory method, the

simulation software IES (Integral Environmental Solution) was used to assess the

performance of the buildings. The result of the study showed that energy reduction was

achieved due to both harnessing of natural ventilation and minimizing of heat gain in line

with applying good shadingdevices alongside the use of double glazing.

Batagarawa (2013), carried out a study ‘ Assessing the Thermal Performance of Phase

Change Materials in Composite hot humid/hot dry Climate’, the aim of the study was to

investigate the possibility of using phase change materials (PCM) in improving indoor

thermal comfort while conserving electricity in office buildings. The study adopted a mixed

method case study and quasi-experimental, using scientifically validated software Design

Builder and EnergyPlus for parametric analysis of simulated result. The result showed that



cooling, lighting and appliance load account for approximately 40%, 12% and 48%

respectively. Simulation results indicated that the magnitude of energy saving can be

achieved by optimizing the passive and climate sensitive design aspects of the building and

an electricity saving of 26%. A review of the literature indicated that a limited number of

studies have examined passive strategies in reducing energy consumption in ICT facilities in

the tropical savanah climate of Nigeria.

Research Methodology

Climate of Study Area

The Koppen climate classification, classified Nigeria into four broad climatic zones namely;

the tropical monsoon climate, the tropical savanna climate or tropical wet and dry, the Sahel

climate or tropical dry climate and Alpine climate or highland climate. In this classification,

Kaduna, the study area falls within the tropical wet and dry climatic region, it experiences

three weather conditions annually and they include a warm, humid rainy season and an

extremely hot dry season, with temperature climbing as high as 400c (104.00F) (Weatherbase,

2017).

The selected case study

To carry out the analysis, a case building was selected within the study climate, which was

the Hephzibah building located in Kaduna along Abuja Street. The building has an east-west

orientation, making it suitable for the passive strategies to be tested. The energy

consumption of the case building is as shown in Table 1.

Table 1: Electricity Consumption Rate of the Case Study

Load(kw/h) cost per one

kw/h(₦ 28)

%

IT equipment 366724.23 10269745.337 59.7

Appliances 48328 1353377.312 7.9

Cooling load 169009.516 4732942.4861 27.5

Lighting load 30,694 859554.776 5.0

Total 614755.23 17215605.461

Source: Authors’ Fieldwork (2017)

This research adopted quasi-experimental research design, through the use of dynamic

simulation as the main investigatory tool. The quasi-experimental design was employed due

to its ability to examine causality which is the aim of this research. By identifying key

variables, computer simulations were used to examine the effect of the variables on



reducing cooling load. Energy simulation software Ecotec was used to examine the

performance of the building selected as a base line model.Five passive strategies were

considered in order to evaluate the collective effect of applying all these strategies on

reducing cooling load in ICT facilities; they include: Double skinned façade, shading,

Double glazing, Materia and Micro climate. The sequence shown in Figure 4was followed to

achieve the desired result.

Figure 4: Sequence for data collection, analysis and result presentation

The data collected from the field survey such as occupancy schedule of the case building,

material schedule and energy consumption. The software Eco-tech requires climatic data to

run a valid simulation in given location, these climatic data were added as separate weather

files input in the software before running the simulation (Stage one of sequence). The data

were input in the simulation software for the base case model and simulated, the result of

cooling load was compared with the one measured on site. (Stage two of sequence). The

stage (three) saw the application of independent variables (Orientation, material, shading,

double glazing and double façade) on the base case model and simulation carried out to

determine the monthly cooling load and the possible energy reduction. The final stage of the

sequence was analysis and result presentation in tables and graphs. It is worthy to note that

the case building was simulated in three (3) scenario. 1) The case building in its present state,

2) with the combination of shading devices, double glazing of windows and light coated

materials .3) double skinned façade.

Results and Discussion

This section consists of simulated results in line with the objective of the study, which is to

evaluate selected passive design strategies in reducing cooling load.

The first scenario simulation was carried out in order to compare the measured in Table.1

and simulated results in Table.2. The difference between the results was found to be less

than 5%, which according to Rahman et al (2008), a difference less than 5% makes the

modelling procedure.

Case Studies Base case models application of independent

variable

Analyse and result

presentation



Monthly Heating/Cooling Loads of the Case Building in its Present State. (Scenario 1)

Max Heating: 0.0 C - No Heating.

Max Cooling: 147.175 kW at 15:00 on 5th May

Table 2: Cooling Result of Existing Building

Figure 5: Monthly Cooling Load for Existing Case Building.

HEATING COOLING TOTAL

MONTH (kWh) (kWh) (kWh)

Jan 0 7911.256 7911.256

Feb 0 11753.733 11753.733

Mar 0 19780.482 19780.482

Apr 0 21314.768 21314.768

May 0 22476.992 22476.992

Jun 0 16245.322 16245.322

Jul 0 11768.221 11768.221

Aug 0 10550.033 10550.033

Sep 0 11958.641 11958.641

Oct 0 17089.055 17089.055

Nov 0 12556.526 12556.526

Dec 0 7104.497 7104.497

TOTAL 0 170509.516 170509.516

PER M² 0 239.782 239.782

0

10000

20000

30000

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Monthly Cooling Load




Simulation of the case study with consideration of some variables (Double glazing,

materials, and Shading devices)

Max Heating: 0.0 C - No Heating

Max Cooling: 75.664 kW at 12:00pm on 11th May

Table 3: Cooling Result on Base-Case Model



Jan 1.67 3869.714 3871.384

Feb 0 6017.76 6017.76

Mar 0 10628.243 10628.243

Apr 0 11754.305 11754.305

May 0 12586.073 12586.073

Jun 0 8615.369 8615.369

Jul 0 6258.722 6258.722

Aug 0 5430.299 5430.299

Sep 0 6230.766 6230.766

Oct 0 9274.935 9274.935

Nov 0 6374.783 6374.783

Dec 0 3524.649 3524.649

TOTAL 1.67 90565.617 90567.289

Source: Authors’ Analysis (2017)

Figure 6: Monthly Cooling Loads of base-line model

Max Heating: 0.0 C - No Heating

Max Cooling: 80.797 kW at 12:00 on 11th May

0

5000

10000

15000


Monthly Cooling Load




Table 4: Cooling Result on Base-Line Model with Double Facade.



Jan 0 4151.354 4151.354

Feb 0 5590.281 5590.281

Mar 0 8864.329 8864.329

Apr 0 9236.464 9236.464

May 0 10365.71 10365.71

Jun 0 7570.45 7570.45

Jul 0 5702.387 5702.387

Aug 0 4880.492 4880.492

Sep 0 5394.458 5394.458

Oct 0 8326.75 8326.75

Nov 0 6556.929 6556.929

Dec 0 3883.93 3883.93

TOTAL 0 80523.531 80523.531

Figure 7 Monthly Cooling Loads of base-line model with double facade.

Discussion

Given that the monthly cooling load of the existing case building as represented in Table 2,

and Figure 5, with the month of May experiencing the highest cooling demand while the

month of January experiencing the lowest cooling demand, the total annual cooling demand

amount to 170509.516 kw/h. It was observed that after the application of the passive

strategies, there was a significant reduction in annual cooling demand as follows: double

glazing 15% amounting to 144933.0886 kw/h, light color coating with high reflectance 11.5%

amounting to 150,900.92166 kw/h, shading devices 26.5% amounting to 125324.49426kw/h

and double skinned façade 47% amounting to 80523.531 kw/h. The combination of double

glazing, light color coating with high reflectance and shading devices saw the reduction in

the annual cooling load by 53% from 170509.516 kw/h to 90565.617 kw/h as shown in Table

0

5000

10000

15000


Monthly cooling load




3 and Figure 6, while double skinned façade reduced by 47% from 170509.516 kw/h to

80523.531kw/h as shown in Table 4 and Figure 7. The result showed that the selected

passive strategies were able to reduce the cooling load, however, double skinned façade was

more effective, reducing about 47% as shown in Figure 8. These findings corroborate

Hannan’s (2013),which showed a significant reduction in energy in residential building by

using passive design strategies.

Figure 8: Reduction of Annual Cooling Load

Conclusions

The energy consumption of a building depends largely on the climatic condition of the

location of a building as shown in Figure 5.There is variation in the monthly cooling load of

the building as a result of the monthly climatic conditions, however with passive design

strategies this study has shown that energy can be reduced. Hence, the study recommends

that architects should integrate passive design strategies as an integral part of design and

architectural expression in reducing the cooling load in hot and dry tropical climate.

double skinned façade

47%

[CATEGORY NAME] 26.5%

double glazing of windows

15%

[CATEGORY NAME] 11.5%

ENERGY REDUCTION



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